1. Field of the Invention
The present invention relates to an image acquisition apparatus which has a focus detection function and performs an image acquisition operation using an electronic image sensor and a program recording medium having recorded therein a program for causing a computer to process an image signal. In particular, the present invention relates to an accurate focus detection technique and a technique for preventing the degeneration of image quality taking noise characteristics into consideration.
2. Description of the Related Art
Conventionally, various techniques are disclosed for an image acquisition apparatus to electronically capture an object image using an electronic image sensor.
U.S. Pat. No. 4,185,191, for example, discloses a technique for a TTL phase-difference detection device. This is a focus adjustment method called the fly lens method. The light flux passed through a lens array is received by a pair of light-receiving elements making up a line sensor, and by processing the signal of this line sensor, the image shift, i.e., the phase difference is calculated. This phase difference is fed back to the displacement of a focusing lens.
Also, Jpn. Pat. Appln. KOKAI Publication No. 10-274562 discloses a technique for the TTL phase-difference detection device employing the re-focus method.
U.S. Pat. No. 6,781,632 discloses a technique in which a group of minuscule lenses for pupil-dividing the light flux passed through an imaging lens and a group of pairs of light-receiving elements for receiving the light flux pupil-divided by the minuscule lenses are partially formed on the image sensor thereby to configure a focus detection area, and the focus is detected in this focus detection area by the phase-difference detection method.